Measuring system for recording absolute angular or position values

ABSTRACT

A measuring system for the recording of angular or position values, wherein the scale includes a measurement track with absolute encoding, and which is scanned by a sensor is provided. The scale is composed of at least two segments with similar absolute encoding, and a suitable track is provided on the scale with which the absolute value of the particular segment reached is calculated by a further sensor arrangement. The total absolute value is then gained from the combination of both absolute values.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of applicationSer. No. 10/116,489, filed Apr. 4, 2002.

The present invention relates to a measuring system for recordingabsolute angular or position values.

Such a measuring system, which is suitable both for angular as well asposition measurements, is well known from DE 195 05 176 A1. Thisspecification describes a linear PRC code (absolute encoding in thescale axis and one after the other in a narrow line with equal spacingof an additional incremental track) whose length is given by L=thedivision * bit value of the absolute code. The incremental track servesthe purpose of increasing the accuracy of the respective absolute valueto be determined.

With a division spacing of, for example, 20 to 30 μm and a 12 bitabsolute track, total lengths of 20 μm to 30 μm*4096≈82 to 123 mmresult. This maximum scale length is far too short for many purposes. Ifscale lengths of, for example, 4 to 5 m are to be implemented, absolutecodes of more than 18 to 20 bits are needed, as indicated in DE 195 05176 A1.

Such scales are complicated to manufacture. Moreover, the 18 to 20photo-receivers must render the scale as distortion free as possible andthis must be illuminated with light of sufficient intensity. Inaddition, complex signal processing is required in the evaluationelectronics.

Incremental length encoders for such a scale length are versatile asregards scale design and evaluation electronics, so that they are alsoused for absolute measurements. To do this, one or several referencemarks are necessary, which must always be approached when the system isswitched on or off. The measuring device is also susceptible to loss ofposition, therefore this must always be taken into account byapproaching the reference marks to ensure the required accuracy. This istime-consuming, not always feasible and is preferred only for costreasons over the rarely encountered and expensive absolute measuringsystems.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a measuring system forrecording absolute values, which can be used for large scale lengths,and which does not require a very large number of bits in the scaleencoding with the associated disadvantages.

With the foregoing and other objects in view, there is provided inaccordance with the invention, a linear measuring system for therecording of angular and position absolute values, where the scaleincludes a measurement track for generating absolute values which isrecorded by an appropriate scanning head, wherein the scale is composedof at least two segments which are identical created for the generationof absolute values and wherein at least one suitable track is providedon the scale for determining the absolute value of the particularsegment reached by means of a further sensor arrangement and whereinmeans of switching are provided which use the absolute value of thesegments and the calculated absolute value within the segment to providethe total absolute value for further processing.

According to another feature of the invention, the at least one suitabletrack is at least one part of the measurement track composed of one ormore tracks.

According to a further feature of the invention, the at least onesuitable track is at least one parallel track applied onto the scale.

According to yet another feature of the invention, the particularsegments are designed with the same code sections.

According to yet a further feature of the invention, the parallel trackis designed for magnetic signal recording.

According to yet another feature of the invention, the parallel trackcontains permanent magnetic segments.

According to yet a further feature of the invention, an auxiliary powerbattery outside and/or inside the further sensor arrangement is providedfor emergency supply.

According to yet another feature of the invention, the measuring systemcomprises at least two identical and staggered scanning heads whosemeasured values are used for redundant signal evaluation by the externalcontrol system.

According to yet a further feature of the invention, the fundamentalabsolute measuring system is based on optical, magnetic, inductive,electromagnetic or capacitive measuring systems or a combinationthereof.

According to yet another feature of the invention, the absolute value ofthe segment reached is determined by logical evaluation of the traversedsegments from a defined starting position.

The linear scale in accordance with the invention may be produced at areasonable cost for any length of linear measurement and is simple touse. The complete scanning sensor's components are suitable foruniversal application in angular and position measuring systems and canbe used for any lengths of measurement. The design of the linearmeasuring device in accordance with the invention takes account of thewide range of requirements and produces a universal and cost-effectivedevice design for even the most diverse of tasks.

The idea behind the invention is to use, for example, 12 bit absoluteencoded segments, which for optical scanning systems are about 10 mm inlength, and a plurality thereof arranged in sequence produce the lengthof the scale. Advantageously these segments contain an absolute encodedtrack, preferably equipped with an additional incremental track runningparallel for analog recording of the path in between, in order toproduce a total absolute value of very high resolution. A 4 m scalecontains approximately 40 such identical absolute encoded segments, forexample, in PRC code, the code design for the beginnings and ends ofwhich is taken into account for the continuous signal evaluation. A12-bit code, for example, will result in 144 possible encodings, afterwhich a cyclic transition to the next segment can take place.

In order to determine the absolute position as a whole, it is necessaryto record the “number” of the particular segment. In accordance with theinvention, this is done by recording the segments according to directionand position, and then identifying them logically from a definedstarting position.

The segments must also be recorded when the main power is switched off,and therefore the consumption of energy or power needs to be low so thatauxiliary power which is suitable for this purpose can be madeavailable, for example via a battery. The power consumption of all ofthe previously known measuring systems for recording absolute values isfar too high for this, typically between 20 mA and more than 200 mA, sothat batteries cannot be used to provide the auxiliary power. Accordingto the invention, therefore a further sensor arrangement with a suitableevaluation circuitry is provided which makes it possible to performcountable recording of segments while the associated expenditure andtherefore the power consumption are kept as low as possible. The designand therefore the power consumption of this further sensor arrangementdepend to a great extent on the type of recording of the absoluteencoded segments to be performed.

If the absolute encoded segments are used for recording the number ofthe segments by means of the further sensor arrangement, this offers theadvantage that the existing measurement track can be used. The sections,which are provided, for example, with a PRC code and designed as 12-bitabsolute encoded sections, offer different possibilities of recordingthe number of sections using the further sensor arrangement. The PRCabsolute track itself, for example, can be used by reducing the absoluterecording to one single sensor, as described in EP 1102040 or U.S. Ser.No. 09/716,338, and leaving out the additional evaluation of theincremental track so that the thereby simplified circuit arrangement forrecording the sections requires as little auxiliary or battery power aspossible.

The incremental track described above, which is advantageously arrangedin parallel to the PRC track, is also suitable for the accuraterecording of the segments by means of the further sensor arrangement.For this purpose, two sensors of the known simple type, for example,which are staggered by 90° (270°), can be used to record the 360°incremental division segment. Countable recording of the incrementalsegment is performed according to direction, and the resultant length ofthe absolute segment (in the case of a 12-bit code, for example, thiscorresponds to 4096 increments) is recorded and used to evaluate thetotal absolute value.

There are different ways in which the absolute segments can be encoded.A simple version is, for example, a segment generating a sin/cos signalof 360° over the entire length (for example, through magnetized N/Ssegments), which can be divided with a correspondingly high resolutionof between 8 bits and 12 bits and more by interpolation. Such absolutesegments arranged in sequence can also be used in a simple way forpower-saving recording of particular absolute segments by using, forexample, the well-known evaluation circuits with two sensors which arestaggered by 90° in the further sensor arrangement.

For each individual absolute segment and for each of its possibledesigns, there are several methods and designs which are suitable forthe further sensor arrangement in order to record the number of segmentsin a more or less power saving way. The limits to the lowest powerconsumption are set here by the absolute encoding selected, and theseare critical to many applications with limited availability of auxiliarypower. In particular in the case of applications which require batteryoperation over 5 . . . 10 years without recharging, the required powermust be decreased to a few μA. In order to ensure this as far aspossible, additional measures are provided by the invention as will bedescribed in the following.

In accordance with a further design of the invention there is, inaddition to the absolute encoded segments, a track, which permits therecording of the segments in 4 sections by interacting with, for examplein its simplest design, two switch sensors, thus clearly determining theposition even for extremely high process speeds. In its simplest typethe track is provided with a symmetrical dark/light track for opticalsystems, or, for magnetic scanning, with a structure havingapproximately 50% of the sections magnetic and non-magnetic, and isadvantageously staggered by 25% of the segments at the beginning and endof the encoded track, respectively. It is recommended to record thetrack magnetically which, by means of a permanent magnet, can providethe auxiliary power for the sensors used for this purpose, and whichfavors battery operation for signal processing and data storage due tothe minimal power consumption. This detection system is also very robustand resistant to dirt. The auxiliary power battery is required to storethe absolute value of the segment, to enable secure recording ofposition immediately after switching on the supply voltage. This alsoguarantees the correct absolute value of the segment when the mainspower is switched on again, if the movable device is adjusted by handwhen there is no mains power. The individual segments and their numbersare co-recorded as absolute values on the parallel track and thus createthe absolute value when the equipment is switched on again.

The absolute value generation in each particular segment achieved inthis way—quite independent of the selected process used for absolutevalue generation—is supplemented by means of the countable recording ofsegments to form the total absolute value for any length of scale. Thesensor components including signal processing are housed in the completesensor. They are the same for a plurality of angular and positionmeasuring systems and are therefore versatile in use. The scale can becreated in “endless length”, the required lengths of scale can simply beseparated from it. Advantageously, the data exchange and parameterizinginterfaces are also designed identical to those of the rotary andangular position encoders, in order to ensure the advantageousend-to-end integration of the sensor systems in customer control systemswith respect to start-up, use and service. Fully digital versions viaSSI data exchange and parameterizing are especially advantageous in thisrespect. Encoder systems, under real-time signal processing inparticular, offer redundant sensor evaluation via parallel retrievableSSI pulse signals on several encoders—each with a separate data line—andmay also be used in a linear measuring system in a very dirtyenvironment (both for the sensor and for the scale).

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a measuring system for recording absolute angular or position values,it is nevertheless not intended to be limited to the details shown,since various modifications and structural changes may be made thereinwithout departing from the spirit of the invention and within the scopeand range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of the scale;

FIG. 2 shows the scale with scanning heads;

FIG. 3 is a schematic view of an embodiment of a measuring systemaccording to the invention;

FIG. 4 is a schematic view of another embodiment of a measuring systemaccording to the invention;

FIG. 5 is a schematic view of a further embodiment of a measuring systemaccording to the invention;

FIG. 6 is a schematic view of yet another embodiment of a measuringsystem according to the invention; and

FIG. 7 is a graph illustrating a signal course over time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a part of a scale 1 which is provided with a track 2encoded with, for example, 12-bit absolute values. This means that theappropriate scanning head comprises an array of twelve scanning cells,each of which recognize a new absolute value after a movement of oneincrement. Three segments 1 a to 1 c are shown here, whereby only anextract of the central segment 1 b can be seen. In one segment there are2¹²=4096 distinct increments present, for example in PRC code. The totalscale is made up of several segments 1 a to 1 c. An incremental track 3is positioned below track 2, and is used to increase the accuracy ofeach of the particular values of the absolute track 2; it has the sametotal length as the scale. Both track 3 and track 2 form the absoluteencoded segments and can be used, individually or in combination withthe further sensor arrangement, for countable recording of the segments.

In addition to the said tracks according to the invention an additionaltrack 4 of the same length as the segments can be provided, which isused to recognize and record the segments and is based on a definedstarting position to logically determine the direction and position ofthe segments. Thus the “number” of individual segments can therefore bedetermined. In its simplest form, the track is equipped with asymmetrical dark/light track for optical systems, or, for a track withmagnetic evaluation, with 50% of the segments having either a magneticor non-magnetic structure. It is important that at the transitionalpoints from one segment to another, for example from 1 a to 1 b, amagnetic structure is present and is located staggered by approximately25% of the segments. This is shown in FIG. 1 where, for the purposes oftrack 4, it may be assumed that segment 1 b is shown in its entirety.Only by doing this can it be shown that 50% of the track is magnetic and50% non magnetic. The track is scanned with, for example, two switchsensors, to determine clearly the point of transition. The switchsensors are positioned advantageously at a distance of approximately 25%of the segment. This allows recording of the 4 quadrants of the segmentsmarked, for example with an x in FIG. 1, (2 times 25% magnetic, 2 times25% non-magnetic), at approximately 2 m/sec, even at a very highmeasuring speed of, for example, 10 m/sec., which is certainlysufficient even for slow sensors such as Reed switches or pulsedmagnetic sensors. This is important for the evaluation of the segmentsto be counted under all sorts of on/off switching operations of thesupply voltage and for the logical composition of the absolute valueusing the segments and necessitates careful design. It is not intendedto further explain here that higher sensor switch speeds would allowthem to be located at much smaller distances than 25% of the segment,for example in an integrated module. Hence, the actual position iscalculated from the absolute value of track 2, enhanced possibly bytrack 3, and the determination of the “numbers” of segments with track4.

The term ‘parallel track’ shall also include those cases in which theencoding of the parallel track provided to determine the number of thesegment superimposes the measurement track, and where the further sensorarrangement only record the encoding assigned to them.

FIG. 2 shows a side view of scale 1 with a number of segments, forexample 1 a to 1 c. There are two staggered scanning heads 5, whosemeasurement results are used for a redundant signal evaluation and areprocessed accordingly in the control system 6.

FIG. 3 shows the scale 1 with the sensor components and an exemplarysignal processing, which includes the sensor 5. The further sensorarrangement 7 is supplied, together with the associated switching means10 of the absolute values of the segments, form the mains power 12 aswell as from an auxiliary power 13, such as a battery, such that duringa mains disconnection the function is maintained and no segmentmeasurement values are lost.

The measurement track 2, 3 detected by the scanning head 8 results inthe generation of the absolute values 9 within the segments and needsonly function when mains-power is provided. The two absolute values 9and 10 are consequently used for generating the total absolute value 11which is provided by 14 for further processing wherein the definedstarting position 15 are taken into account.

FIGS. 4 to 6 show various scales with absolute measuring tracks and therespectively assigned arrangement of the scanning head 8 for an absoluterecording within the segment and the further sensor arrangement 7 forforming the absolute value of the segments. This signal processing isaccomplished in the same manner as described above for the embodimentshown in FIG. 3.

FIG. 7 illustrates the operating mode of the exemplary advantageousscale shown in FIG. 6. The embodiment shown in FIGS. 4 to 7 have alreadybeen explained in detail in the description above and therefore nofurther explanations are necessary.

1. A linear measuring system, comprising: a scale including at least twosegments identically created for the generation of absolute values, eachof said at least two segments including a measurement track forgenerating the absolute value within said segments being recorded by anappropriate scanning head, and at least one suitable track being atleast one part of said measurement track for determining the absolutevalue of the particular segment reached by a sensor arrangement; and aswitching device using the generated absolute value within said segmentsand the determined absolute value of said segment to provide the totalabsolute value for further processing.
 2. The measuring system accordingto claim 1, wherein said at least one suitable track is composed of oneor more tracks.
 3. The measuring system according to claim 1, whereinsaid segments are constructed with the same code sections.
 4. Themeasuring system according to claim 1, further comprising an auxiliarypower battery outside or inside said sensor arrangement for emergencysupply.
 5. The measuring system according to claim 1, comprising atleast two identical and staggered scanning heads whose measured valuesare used for redundant signal evaluation by an external control system.6. The measuring system according to claim 1, wherein the measuringsystem is based on at least one system selected from the groupconsisting of an optical, a magnetic, an inductive, an electromagneticand a capacitive measuring system.
 7. The measuring system according toclaim 1, wherein the absolute value of said segment reached isdetermined by logical evaluation of traversed segments from a definedstarting position.
 8. The measuring system according to claim 1, whereinthe absolute value of the segments and the determined absolute valuewithin the segment are linear values.
 9. The measuring system accordingto claim 1, wherein the absolute value of the segments and thedetermined absolute value within the segment are angular values.